Drying method and apparatus



Oct. 18, 1960 c. w. GORDON 2,956,347

DRYING METHOD AND APPARATUS Filed July 23, 1957 28 Vent Fun r: i i

T Fine Dry Cool 20 Cool In Fine'Wet l CoallFeed 1 Air Tampering Dumper Clusslfler 32 34 3/ I CoorsZeWet T Cool Feed 3 1 Coarse Dry Cool X Air Heater i INVENTOR Charles W. Gordon (2%. A. fab

' ATTORNEY United States Patent DRYING METHOD AND APPARATUS Charles W. Gordon, Glen Ellyn, 111., assignor to Combustion Engineering, Inc., New York, N.Y., a corporation of Delaware Filed July 23, 1957, Ser. No. 673,689

'3 Claims. (Cl. 34-10) This invention relates to a method of drying particulate material and has particular relation to a method of drying such material wherein the material is subjected to a hot drying gas stream with the method being particularly well adapted for the drying of coal.

In the processing of coal as Well as other particulate materials, such as ores, it is customary to subject the material to streams or baths of Water, as for example, in the washing operation, and in the upgrading operation by means of the flotation method. These operations leave the coal with a substantial water content which is undesirable for many reasons and a majority of which is removed prior to shipment of the material.

There have been many methods and apparatuses employed for drying this coal and the method of the present invention involves an improvement which results in a more elfcient drying operation. In accordance with the present invention the drying is accomplished by introducing the particulate coal or other material directly into a stream of hot drying gases in a particular manner, with the material, of course, being of a certain size range, as, for example, the material may be comprised of particles within the range of 1 A in. to zero. The gases are heated by a suitable heater after which they are directed through a horizontal conduit and then into a cyclone. The gases pass out of the upper end of the cyclone and into a vertical conduit which leads into another cyclone through which the gases pass. The velocity of these gases passing through these horizontal and vertical conduits is such that the material above a particular particle size that is well within the limits of the range of particle size of the material, as for example above f of an inch, will not be entrained in the gas stream while below this particle size the material will be entrained in the gas stream. The material to be dried is divided into two portions above and below this particular particle size with the coarse fractions or the material above this size being introduced into the horizontal duct or conduit. Although the gas velocity through this conduit is not sufiicient to entrain the material in the gas stream it will cause the material to move along the conduit toward the cyclone and the material is introduced into this horizontal conduit at a point such that it will be subjected to the drying gases for a sutficient time to remove a substantial portion, although preferably not all, of the moisture from the material. In the cyclone this coarse material is separated from the drying gases and the gases which are now somewhat cooler than originally and which also contain the moisture from the coarse fractions pass up through the vertical drying duct or conduit. Into this duct is introduced the less coarse coal fractions or in other words, the material below said predetermined particle size, with this material being entrained in the upwardly flowing gas stream and being contacted by it for a sufficient length of time to remove a substantial portion, but preferably not all, of the moisture from the material. The drying gas with this material entrained in it passes into the cyclone separator ice Where the material is separated from the gas. The coarse fractions of the material do not absorb as much moisture in the various processing operations as the fine fractions and therefore are more easily dried. Thus although not as intimate contact between the material and the drying gases is had in the horizontal drying conduit as would be the case if there were entrainment, there is suflicient contact to adequately dry the coarse coal fractions so that only the finer coal fractions need be entrained within the stream of drying gas and therefore the velocity of the drying gas and accordingly the power necessary to produce such velocity needs to be only sufficient to entrain these finer coal fractions to provide intimate contact of these coal fractions with the drying gas.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawing wherein the single figure is a diagrammatic representation of a structural organization for carrying out the method of the invention.

Referring now to the drawing, the system disclosed therein comprises heat exchanger 10 which may be in the form of an air heater that is fired with a suitable fuel and which is effective to heat a stream of air which is directed outwardly through the upper end of the heat exchanger and through the conduit 12 extending there from. Connected to conduit 12 is the generally horizontal drying conduit or duct 14 which extends into the cyclone 16. This cyclone has the usual rotatable air look at 18 at its lower end and connected with the upper end of the cyclone is the vertically directed drying conduit or duct 20 which leads into the cyclone 22 and which latter cyclone also has a conventional air lock 24- and is connected at its central portion with the vent fan 26 through conduit 28. This fan 26 is effective to draw the hot air for drying from air heater 10 through the dr ing conduits 14 and 20.

The coal that is to be dried in the drying system consists of particles of various sizes within a particular range. This coal is separated or classified into two groups above and below a particular size with the coarse coal fractions being introduced into the horizontally directed gas stream passing through conduit 14 while the finer coal fractions are introduced into the vertically directed gas stream passing through conduit 20. Fan 26 is of a sufficient capacity and is operated so that the velocity of flow through conduit 20 is sufficient to entrain the fine coal fractions that are introduced thereinto within the upwardly flowing stream of gas while the velocity of the gas flowing through conduit 14 is not suflicient to entrain the coarse coal fractions introduced into conduit 14 but is sufiicient to move these fractions along the horizontally directed conduit into cyclone 22. The location of the introduction of the coarse coal fractions into conduit 14, which location is generally designated 30, is a sufficient distance from cyclone 16 so that the coarse coal fractions have a major portion of the moisture removed from them prior to reaching this cyclone. In the cyclone these coarse coal fractions are separated from the drying gas with the coarse coal fractions falling to the bottom of the cyclone and passing out through rotating air lock 18 while the drying gases pass out the top of the cyclone and into the vertically disposed conduit 20. The fine coal fractions are introduced into conduit 20 at the .7 3 location designated generally 31, are entrained in the upwardly flowing gas stream and are conveyed by the gas stream mto separator cyclone 22 where these fine coal fractions are,-separatedfrom the drying gas passingout thej bottom of the cyclone through airlock; 2,4 while'the drying gas passes out the top of the cyclone through condult 28 and fan 26. it 7 'As .an example of this operation, if the coal 'has a particle size range of 1 A" to 0, which is a common range in the coal industry, the fractions from 1%" to rnay be introduced into and dried within conduit 14 while the fractions from to zero may be introduced into and dried within conduit 20.

As mentioned hereinbefore the coarse coal fractions are more easily dried than the fine coal fractions ;and accordingly need not be so intimately contacted with the drying gases. Thus although the coarse fractions are not entrained within the drying gases as are the fine coal fractions and accordingly do not come into as intimate contact with the drying gases as the fine coal fractions they are nevertheless adequately dried.

Since bone dry material and particularly coal presents a dustproblem during handling it is desirable to leave a certain percentage of moisture in the coal to alleviate this situation with 3% moisture being satisfactory for this purpose.

If desired additional hot drying gas may be introduced into the lower end of conduit 20 in order to increase the temperature of the gasespassing through this conduit as well as to add gas of less moisture content than that passing from cyclone 16 and for this purpose conduit 32 may be interconnected between the lower end of conduit 20 and conduit 12. In order to control the delivery of gases through conduit 32 and conduit 14 and to proportion the flow through these conduits as desired suitable control valves 34 may be provided. This addition of hot dry gas to conduit may be desirable in certain instances to increase the drying ability of the stream of gas passing up through this conduit and into which the fine coal fractions are introduced.

With the method of this invention the velocity of the stream of drying gases through conduit 14 and 12 may be maintained at a minimum and below that required to entrain the coarse coal fractions so that the power required to operate the system may be maintained at a and yet an eflicient drying operation obtained.

It will be understood that the above description is intended for the purpose of illustration only and that modifications such as will occur to those skilled in the art are possible and are embraced within the scope and spirit of the invention.

What is claimed is:

1. The method of drying coal comprising providing'a stream of hot drying gases directed horizontally and then vertically, classifying the coal by separating it into two groups above and below that which will just be en- 4 trained in the gases introducing the coal fractions which are sufficiently large that they will not be entrained in the stream into the horizontal run thereof and in sufficient contact with the gas to remove a major portion of the moisture from said fractions, thereafter separating these coal fractions from the horizontal run of said stream, and introducing into the vertical run of the gas stream the coal fractions which-are sufficiently small so that they will be entrained in said stream and contacting these gases with these fractions sufi'iciently to remove a major portion of'the moisture from the fractions and thereafter separating the fractions from the gas stream.

2. The method of'drying moist discrete coal of a particular range of particle size comprising classifying the coal by separating it into two groups one containing the fine coal fractions and the other containing the coarse coal fractions providing a stream of hot drying gas the velocity of which, is sufiicient to entrain fine coal fractions within this range but not suflicient to entrain coarse coal fractions within' the range, introducing said coarse coal fractions into said stream and retaining them therein a sufiicient time to remove most of the moisture from the coal, then separating these coarse coal fractions fro-m the stream, introducing additional hot drying gas to the eflluent stream from said drying the coarse coal fractions and introducing said fine coal fractions into the resulting stream, retaining these fine fractions in this stream a suflicient time to remove most of the moisture therefrom and thereafter separating the same from said stream. I

3. The method of drying coal of a range of particle sizes from 1%" to 0 comprising separating the fractions in the range of to zero from the coarser fractions providing a stream of hot drying gases directed horizon tally and then vertically with the velocity of the vertical run being only sufiicient to entrain coal fractions of about and below, introducing the coal fractions above into the horizontal run of said stream and in sufficient contact with the gas to remove a major portion of the moisture therefrom, thereafter separating these coal fractions from this horizontal'run of said stream, introducing into the vertical run of the gas stream the coal fractions below and contacting these gases with these fi'actions sufficient to remove a major portion of the moisture from the fractions and thereafter separating these fractions from the gas stream.

References Cited in the file of this patent UNITED STATES PATENTS 2,156,924 Schneider May 2, 1939 2,235,748 Hukill Mar. 18, 1941 2,450,843 Sherman Oct. 5, 1948 FOREIGN PATENTS 215,812 Great Britain May 19, 1924 

